1. Field of the Invention
The present invention relates to a valve timing control device for modifying the opening and closing timing of an intake valve or an exhaust valve making contact with cams fixed on an intake camshaft or an exhaust camshaft of an internal-combustion engine (hereafter, referred as an engine).
2. Description of the Prior Art
Various types of solutions have been proposed for conventional valve timing control devices. The majority of the proposition includes a housing of rotating in synchronization with a driving force transmitting means transmitting a driving force from a crankshaft of the engine to an intake camshaft and an exhaust camshaft, a case fixed on the housing and having a plurality of shoes which are projected inwardly to form a plurality of hydraulic pressure chambers, and a rotor fixed on an end of the intake camshaft or the exhaust camshaft and having a plurality of vanes to divide the hydraulic pressure chambers into advance side hydraulic pressure chambers and retardation side hydraulic pressure chambers, for example. A hydraulic pressure is provided to and discharged from the advance side hydraulic pressure chamber and the retardation side hydraulic pressure chamber due to an oil control valve. (hereafter, referred as OCV) and the rotor rotates relatively at a required angle with respect to the case. In this way, it is possible to variably control the phase of the intake camshaft or the exhaust camshaft and to modify the opening and closing timing of the intake valve and the exhaust valve as appropriate according to any operation conditions.
Most of the conventional valve timing control devices have a lock mechanism for locking the rotor, which is fixed on an end of the camshaft, in relation to the case rotating in synchronism with the crankshaft at a reference position on starting the engine. The lock mechanism includes a fitting hole arranged at any one hand of the rotor or the case, a lock member arranged at the other hand and fit in the fitting hole to lock the rotor in relation to the case at any one of the maximum advanced side and the maximum retarded side positions, and a push member of pushing the lock member in a direction of fitting the lock member in the fitting hole at all times. With the conventional construction, the initial operation direction of the rotor was limited to only retardation direction or only advance direction.
However, if it is possible to operate the rotor of the valve timing control device from the reference position (hereafter, referred also as a lock position) on starting the engine toward the advance side and the retardation side without the limitation of only one direction such as the retardation direction or the advance direction, it is a foregone conclusion that such a device will have improved versatility.
An intermediate position lock type of the valve timing control device is therefore proposed. With the device, the lock position is set to an approximately intermediate position apart from both of the maximum advanced side position and the maximum retarded side position. It is possible to operate the rotor from the lock position to the advance side and the retardation side.
However, the intermediate position lock type of the valve timing control device has typical problems derived from the typical construction, which is different from the conventional valve timing control devices such as the maximum advanced side position lock type or the maximum retarded side position lock type.
First, with the maximum advanced side position lock type or the maximum retarded side position lock type of the valve timing control device, when the lock member is able to fit in the fitting hole, a hydraulic pressure is applied on the rotor to press the rotor toward the lock position. Here, contact of one of the vanes of the rotor is ensured with one of shoes of the case at the maximum advanced side position or the maximum retarded side position. Therefore, since no force is applied on the lock member, the lock member does not catch on with the other parts. Further, with the conventional valve timing control device, even if a hydraulic pressure in the device is reduced when operation oil is consumed by operation of the device or when a hydraulic pressure passage in the OCV side becomes narrow in a hydraulic pressure supply mode of the OCV side (hereafter, referred as OCV intermediate retained mode) for keeping the rotor with respect to the case at the intermediate position on normal operation, the lock member does not fit or catch on or engage between the maximum advanced side position and the maximum retarded side position because the fitting hole is arranged at the maximum advanced side position or the maximum retarded side position. Since the lock member does not catch on or engage with the fitting hole, the valve timing control device is not disabled during normal operation or in an intermediate retained state.
On the other hand, with the intermediate position lock type of valve timing control device, the fitting hole is arranged at an approximately intermediate position apart from both of the maximum advanced side position and the maximum retarded side position. First, when the rotor is held with respect to the case at the about intermediate position due to the hydraulic pressure supplied from the OCV, the hydraulic pressure passage in the OCV side narrows when in the OCV intermediate retained mode. A hydraulic pressure in the advance side hydraulic pressure chamber or the retardation side hydraulic pressure chamber and a release hydraulic pressure chamber is therefore substantially reduced to one half of the hydraulic pressure in the OCV and the release hydraulic pressure is not sufficient. As a result, the lock member sometimes catches on in or fitted in the fitting hole. In this case, there is a problem that the lock member and the fitting hole undergo wear which reduces their durability, and that the valve timing control device becomes incapable of operation from the intermediate retained state.
Second, when the lock member is operated beyond the fitting hole as the intermediate lock position and the release hydraulic pressure is reduced associated with the reduction of the hydraulic pressure in the advance side hydraulic pressure chamber or the retardation side hydraulic pressure chamber which is generated by consuming the operating oil used for the operation of the device, the lock member pops up due to the pushing force of the pushing member under operation condition and catches on in the fitting hole to prevent operation.
Accordingly, it is an object of the present invention to provide a valve timing control device being a type of locking a rotor at a intermediate position defined between the maximum advanced side and the maximum retarded side with respect to a case, which can reliably control the operation of a lock member to resolve the problems described above.
In order to achieve the object of the present invention, a valve timing control device for modifying the opening and closing timing of an intake valve or an exhaust valve making contact with cams fixed on an intake camshaft or an exhaust camshaft of an internal-combustion engine, comprises a housing rotating in synchronization with a driving force transmitting means transmitting a driving force from a crankshaft of the internal-combustion engine to an intake camshaft and an exhaust camshaft; a case fixed on the housing and having a plurality of shoes which are projected inwardly to form a plurality of hydraulic pressure chambers; a rotor fixed on an end of the intake camshaft or the exhaust camshaft and having a plurality of vanes to divide the hydraulic pressure chambers into advance side hydraulic pressure chambers and retardation side hydraulic pressure chambers; a fitting hole arranged on one of the rotor or the case; a lock member arranged on the other of the rotor or the case and fit in the fitting hole to lock the rotor in relation to the case at an approximately intermediate position apart from both of the maximum advanced side position and the maximum retarded side position; and a push member normally biasing the lock member in a direction of fitting the lock member in the fitting hole, wherein a release hydraulic pressure for releasing the fitting state of the lock member in the fitting hole against the push force of the push member is set to be higher than a lock hydraulic pressure for allowing the fitting state of the lock member in the fitting hole. In this way, a load of the pushing member corresponding to the lock hydraulic pressure can be previously set to a low level. It can therefore reliably prevent an operational failure of the device even if a hydraulic pressure in the device is reduced by the OCV intermediate retained mode or even if the operation oil is consumed by operation of the device. The operational failure of the device generates when the lock member pops up from the fitting hole due to the pushing force of the pushing member to catch on or engage in the fitting hole.
The lock hydraulic pressure may be set to be nearly equal to or lower than a hydraulic pressure of generating a torque generated in the device, the torque being equal to a cam-torque during internal-combustion. In this way, even under a minimum hydraulic pressure condition such as high temperature oil or idle rotation for example, even in the intermediate retained state, it can obviate the inconvenience of fitting the lock member in the fitting hole or getting trapped therein. As a result, the operation of the lock member can be reliably controlled.
The present invention may further comprise first and second communication passages, wherein the first communication passage communicates a backward pressure chamber, in which the push member is arranged, to the advance side hydraulic pressure chamber or the retardation side hydraulic pressure chamber as an operational hydraulic pressure chamber of operating the device, and wherein the second communication passage communicates the backward pressure chamber to outside the device. In this way, since a backward pressure can be applied to the lock member in a releasing operation, the release hydraulic pressure can be set to be higher than the lock hydraulic pressure. Since the release operation can be also delayed, discharge of air remaining in each passage and each chamber in the VVT can be ensured through the first and second communication passages to the outside on starting the engine. As a result, release operations, which are not predetermined and result from residual air, can be reliably prevented.
The first communication passage may be formed at an end of the case in an axial direction of the case. In this way, it is possible to easily process the first communication passage. It is also possible to shorten the length in the minimum cross sectional area of the first communication passage to reduce passage resistance in the first communication passage. It is further possible to perform the release operation of the lock member with stability.
The first communication passage may be a branch of a hydraulic pressure supply passage of communicating the operational hydraulic pressure chamber to a release hydraulic pressure chamber. In this way, it is possible to easily process the first communication passage and to reduce passage resistance in the first communication passage.
The cross sectional area of the first communication passage may be set to be larger than that of the second communication passage. In this way, since the backward pressure can be surely applied to the backward pressure chamber, the release hydraulic pressure can be set to be higher than the lock hydraulic pressure.
The cross sectional area of the second communication passage may be set to be larger than that the cross sectional area allowing discharge of foreign materials. In this way, since foreign materials in drain oil can be surely discharged from the backward pressure chamber to the outside, it can prevent the second communication passage from being blocked by the foreign materials and can ensure reliable operation of the lock member.
The driving force transmitting means may be a chain, the lock member may move in a radial direction of the device, and a stopper may be arranged at the outermost section of the device, the stopper of holding the push member in the backward pressure chamber and integrated with the second communication passage. In this way, the backward pressure in the backward pressure chamber is drained directly to the outside without the passage resistance due to the passage length or diameter. A stable difference between the release hydraulic pressure and the lock hydraulic pressure can be predetermined even if air is mixed in oil in the hydraulic pressure chamber such as an advance side hydraulic pressure chamber.
A valve timing control device for modifying opening and closing timing of an intake valve or an exhaust valve making contact with cams fixed on an intake camshaft or an exhaust camshaft of an internal-combustion engine, may comprise a housing rotating in synchronization with a driving force transmitting means transmitting a driving force from a crankshaft of the internal-combustion engine to an intake camshaft and an exhaust camshaft; a case fixed on the housing and having a plurality of shoes which are projected inwardly to form a plurality of hydraulic pressure chambers; a rotor fixed on an end of the intake camshaft or the exhaust camshaft and having a plurality of vanes to divide the hydraulic pressure chambers into advance side hydraulic pressure chambers and retardation side hydraulic pressure chambers; a fitting hole arranged on one of the rotor or the case; a lock member arranged on the other of the rotor or the case and fit in the fitting hole to lock the rotor in relation to the case at an approximately intermediate position apart from both of the maximum advanced side position and the maximum retarded side position, the lock member including a head section fitting the fitting hole and a flange section having a diameter larger than the head section; a push member pushing the lock member in a direction fitting the lock member in the fitting hole at all times; and a seal member for stopping the flow of operational oil between the advance side hydraulic pressure chamber and the retardation side hydraulic pressure chamber, wherein the seal member may be arranged so as to apply a hydraulic pressure from the retardation side hydraulic pressure chamber on the flange section of the lock member, and to apply a hydraulic pressure from the advance side hydraulic pressure chamber on the head section and the flange section of the lock member. In this way, even if an active release hydraulic pressure is reduced on selecting the OCV intermediate retained mode, it can apply the release hydraulic pressure on larger area of the lock member to ensure release of the lock member and to ensure stable operation of the device.